FIG. 1 is a block diagram showing the configuration of a projector in which brightness is adjusted according to the average luminance level and the state of the luminance distribution of an image signal that is received as input such as is disclosed in Patent Document 1 (WO2012/095945A1).
Upon the reception of an image signal that indicates an image, projector 1 shown in FIG. 1 projects the image that is indicated by the image signal upon a projection surface such as a screen. Projector 1 includes: image input unit 10, resolution conversion unit 20, video output unit 30, light source control unit 40, light source unit 50, LCD (Liquid Crystal Display) drive unit 60, projection lens 70, and CPU (Central Processing Unit) 80.
Image input unit 10, resolution conversion unit 20, video output unit 30, light source control unit 40, light source unit 50, LCD drive unit 60, and CPU 80 are connected by way of a serial or parallel system bus 90.
Image input unit 10 is provided with a signal-determining unit 101, and resolution conversion unit 20 is provided with frame memory 201. Video output unit 30 is provided with image signal detection unit 301, image quality improvement circuit 302, γ correction unit 303, entire conversion unit 304, and light source control unit 40 is provided with SUB CPU 401.
Image input unit 10 receives various image signals that are applied as input to projector 1, for example, a digital image signal such as an HDMI (High-Definition Multimedia Interface) (registered trademark) signal, a DisplayPort signal, and a DVI (Digital Visual Interface) signal or an analog image signal such as a D-SUB signal or a video signal such as a composite video signal and an S video signal.
Image input unit 10 converts theses video signals to a parallel image signal (an RGB signal or a color-difference YCbCr signal) having 8-bit or 10-bit gradation and transmits the result to resolution conversion unit 20. The decoding of a clock signal and horizontal synchronizing signal, vertical synchronizing signal, and parallel image signal data enable signal that are synchronized with the parallel image signal data is carried out in image input unit 10. Signals are converted to a parallel image signal using dedicated LSI (Large-Scale Integration) (not shown in the figures) that is provided in the image input unit, for example, a D-SUB signal being converted to a parallel image signal using an image-dedicated AD converter, a Video signal being converted to a parallel image signal using a Video decoder, and HDMI input being converted to a parallel image signal using an HDMI receiver.
Signal-determining unit 101 that is provided in image input unit 10 has a circuit for acquiring input resolution information of an image signal that is received as input in projector 1. The circuit that is provided in signal-determining unit 101 is made up from a counter circuit of multiple bits and acquires, from the parallel image signal data that have been converted by, for example, the above-described image dedicated AD converter or HDMI receiver, horizontal synchronizing signal, vertical synchronizing signal, and parallel image signal data enable signal, input resolution information that includes at least the following content:
The frequency of a horizontal/vertical synchronizing signal
Vertical synchronizing signal: the number of horizontal synchronizing signals in one cycle
Horizontal synchronizing signal: the number of data signals in one cycle
Horizontal/vertical data valid interval
Clock frequency
Resolution conversion unit 20 carries out the conversion of image signals in accordance with the output resolution. The image signals that are transmitted from image input unit 10 are of various resolutions, and in addition, the output resolution of projector 1 is of uniform fixed resolutions such as WUXGA, WXGA, and XGA, and as a result, the process of converting the resolution of an image signal in accordance with the output resolution is carried out in resolution conversion unit 20. A reducing process is performed when the resolution of the image signal that is received is greater than the resolution of the image signal that is to be supplied as output, and an enlarging process is carried out when the resolution of the image signal that is received is smaller than the resolution of the image signal that is to be supplied as output.
Frame memory 201 that is provided in resolution conversion unit 20 is used for holding several frames of the parallel image signal data from image input unit 10 for carrying out the enlarging/reducing process by resolution conversion unit 20. For example, when the frequency of the vertical synchronizing signal that is indicated in the input resolution information is 30 Hz and an image signal for which the frequency of the vertical synchronizing signal is 60 Hz is to be supplied as output, parallel image signal data for at least a one-frame portion must be held. A large-scale memory is necessary to hold this parallel image signal data. Frame memory 201 is also referred to as a “frame buffer.”
Video output unit 30 has the object of performing adjustment of the white balance and color tone of parallel image signal data that are synchronized with the horizontal synchronizing signal and vertical synchronizing signal of the output resolution that were converted in resolution conversion unit 20 and converts and supplies an image signal by means of image signal detection unit 301, image quality improvement circuit 302, γ correction unit 303, and entire conversion unit 304. The operation of each unit is as described hereinbelow.
Image signal detection unit 301 detects image input information such as the average luminance level or luminance distribution for each frame for image signal data from resolution conversion unit 20.
Image quality improvement circuit 302 uses contour correction technology that uses an optical illusion of human vision known as the Craik-O'Brien Effect to improve contrast.
γ Correction unit 303 is a block that subjects the image signal from resolution conversion unit 20 to brightness adjustment for each single color and typically performs processing according to the following formula.output=255×(input÷255)(1/γ) 
Entire conversion unit 304 performs conversion of the overall color tone of projector 1 and typically performs processing according to the following formula.
                              (                                                                      R                                      01                    ⁢                                          (                                              x                        ,                        y                                            )                                                                                                                                            G                                      01                    ⁢                                          (                                              x                        ,                        y                                            )                                                                                                                                            B                                      01                    ⁢                                          (                                              x                        ,                        y                                            )                                                                                                    )                =                                            (                                                                                          C                      11                                                                                                  C                      21                                                                                                  C                      31                                                                                                                                  C                      12                                                                                                  C                      22                                                                                                  C                      32                                                                                                                                  C                      13                                                                                                  C                      23                                                                                                  C                      33                                                                                  )                        ⁢                          (                                                                                          R                                              i                        ⁢                                                                                                  ⁢                        1                        ⁢                                                  (                                                      x                            ,                            y                                                    )                                                                                                                                                                                G                                              i                        ⁢                                                                                                  ⁢                        1                        ⁢                                                  (                                                      x                            ,                            y                                                    )                                                                                                                                                                                B                                              i                        ⁢                                                                                                  ⁢                        1                        ⁢                                                  (                                                      x                            ,                            y                                                    )                                                                                                                                )                                +                      (                                                                                B                    r                                                                                                                    B                    g                                                                                                                    B                    b                                                                        )                                              [                  Numerical          ⁢                                          ⁢          Expression          ⁢                                          ⁢          1                ]            
Here, Ri1(x, y), Gi1(x, y), and Bi1(x, y) are the input signals of the image that is to be converted, C11-C33 are matrix coefficients, Br, Bg, and Bb are offset coefficients, and R01(x, y), G01(x, y), and B01(x, y) are the output signals of the image that has been converted.
Light source control unit 40 controls the light quantity of projected image light that is supplied by light source unit 50. This light quantity control will be described in the explanation of light source unit 50.
FIG. 2 shows the configuration of light source unit 50.
Light source unit 50 includes: iris 503; rod integrator 504; lamp 510; dichroic mirrors 522 and 523; mirrors 524, 531, and 532; LCDs 541-543; and cross-dichroic prism 550.
The light quantity of white light that is emitted by lamp 510 is controlled by iris 503. Iris 503 is provided with an opening that can be opened and closed, and the control of the opened/closed state of the opening is performed by the above-described light source control unit 40. White light, for which the light quantity is controlled by iris 503, is first made uniform by rod integrator 504 and then irradiated into dichroic mirror 522. Dichroic mirror 522 reflects the light of blue wavelength (B light) and allows the passage of light of wavelengths other than blue, and the reflected B light is turned back by mirror 531 to illuminate LCD 541.
The light that passes through dichroic mirror 522 is irradiated into dichroic mirror 523. Dichroic mirror 523 reflects light of green wavelength (G light) and allows the passage of light of wavelengths other than green, and the reflected G light illuminates LCD 542.
Light from which both B light was extracted by reflection by dichroic mirror 522 and G light was extracted by reflection by dichroic mirror 523 and that has passed through dichroic mirror 523 becomes chiefly light of the red wavelength (R light). R light that has passed through dichroic mirror 523 is turned back by mirrors 524 and 532 to illuminate LCD 543.
LCDs 541-543 that serve as image-forming elements form images of B light, G light, and R light, respectively, and form image light of B light, G light, and R light by being illuminated by light of each color. The image light of each of these colors is combined by cross-dichroic prism 550 and projected by projection lens 70.
LCD drive unit 60 drives each of LCDs 541-543 in light source unit 50 in accordance with an image signal from video output unit 30 and causes the generation of image light.
Projection lens 70 projects the image light that was generated in light source unit 50 upon a projection surface.
CPU 80 carries out the coefficient settings required for conversion for performing resolution conversion (such as enlarging/reducing processing and frequency conversion processing) that is carried out in resolution conversion unit 20 on the basis of input resolution information that was acquired in signal-determining unit 101. In addition, CPU 80 periodically acquires image input information (average luminance level and luminance distribution) that is detected by image signal detection unit 301 by way of system bus 90 and transmits to light source control unit 40 control data for performing iris opening/closing control of iris control unit 503 in light source unit 50.
SUB CPU 401 that is provided in light source control unit 40 receives control data that are transmitted from CPU 80 by way of system bus 90 and generates a control signal for carrying out the iris opening/closing control of iris control unit 503 in light source unit 50.